1. Field of the Invention
The present invention relates to a fuel injection apparatus and applied to a diesel engine, etc. equipped with an accumulator fuel injection apparatus, the apparatus being composed such that high pressure fuel pumps are provided each of which compresses fuel introduced into a plunger room to high pressure by a plunger fitted in a plunger barrel and reciprocated by means of a fuel cam to supply the compressed fuel to a common rail, and the high pressure fuel accumulated in the common rail is injected periodically at determined injection timing into each of the cylinders of the engine.
2. Description of the Related Art
An accumulator fuel injection equipment used in a diesel engine is provided with a plurality of high pressure fuel injection pumps each of which compresses fuel introduced into a plunger room to high pressure by a plunger fitted in a plunger barrel and reciprocated by means of a fuel cam. The high pressure fuel accumulated in a common rail is supplied to each of fuel injection valves to be injected periodically at determined injection timing into each engine cylinder.
In an accumulator fuel injection apparatus for the diesel engine like this, discharge duration of high pressure fuel from each of the high pressure fuel pumps is controlled by controlling opening/closing of a low pressure side fuel feed passage by means of an electromagnetic valve provided to each of the high pressure fuel pumps as disclosed for example in Japanese Laid-Open Patent Application No. 64-73166 (patent literature 1) and Japanese Laid-Open Patent Application No. 7-217515 (patent literature 2).
According to the art disclosed in the patent literature 1, fuel introduced into a plunger room of each of a plurality of high pressure fuel pumps is compressed to high pressure by a plunger and supplied to a common rail by closing a fuel feed passage to the plunger room by an electromagnetic valve while the plunger is in the up stroke. The electromagnetic valve is then opened when the plunger moved up near to its top dead center and fuel is introduced in the plunger room as the plunger moves down.
The patent literature 2 relates to improvement of the electromagnetic valve of the high pressure fuel pump, in which the electromagnetic valve is increased in responsivity by making it possible to reduce spring force to retain valve body opened; by allowing force to be reduced which exerts on the valve body in direction to close the valve when fuel-back flows through the valve.
In the prior art disclosed in the patent literature noted above, an electromagnetic valve is provided for each of high pressure fuel pumps for pressure feeding fuel to a common rail, and fuel introduced in the plunger room of high pressure fuel pump is compressed to high pressure and discharged to the common rail by closing each electromagnetic valve by a signal form a controller, or high pressure fuel remaining in the plunger room is spilled to a fuel feed passage side by opening the electromagnetic valves by a signal from the controller.
Therefore, as an electromagnetic valve is provided for each of the high pressure fuel pumps and a controller for controlling the electromagnetic valve is provided, devices for controlling fuel discharge and spill become complicated requiring a number of parts and resulting in increased cost. Further, the likelihood of occurrence of a malfunction in the electronic components of the electromagnetic valves and electronic controller for controlling fuel discharge or introduction is higher as compared with a mechanical control device.
Furthermore, as control of fuel discharge and spill is done by electromagnetic valves provided for each of the fuel pumps and a controller in the prior arts, time retard inevitably occurs from the time of detection of engine operation conditions to the time to actuate the electromagnetic valve by means of the controller when starting the engine. Thus, the period of starting the engine may be increased resulting in deteriorated engine startability.